Nonaqueous secondary battery functional layer composition, nonaqueous secondary battery functional layer, and nonaqueous secondary battery

ABSTRACT

A composition for a non-aqueous secondary battery functional layer including a particulate polymer, wherein the particulate polymer is a copolymer containing 20% by weight or more and 80% by weight or less of an aromatic monovinyl monomer unit; and 0.01% by weight or more and 2% by weight or less of a polyvalent ethylenically unsaturated crosslinkable monomer unit, a volume-average particle diameter D of the particulate polymer is 0.5 μm or more and 5 μm or less, and a swelling degree of the particulate polymer to an electrolyte solution is more than 1 time and 3 times or less; and a non-aqueous secondary battery including the same.

FIELD

The present invention relates to a composition for a non-aqueoussecondary battery functional layer, a functional layer for a non-aqueoussecondary battery, and a non-aqueous secondary battery.

BACKGROUND

A secondary battery is a generic name for batteries havingcharacteristics that they are capable of being repeatedly charged anddischarged. The secondary battery generally includes a positiveelectrode, a negative electrode, a separator, an electrolyte solution,and a sheathing material. The electrolyte solution is filled into aspace formed by the sheathing material. A secondary battery including anon-aqueous electrolyte solution as the electrolyte solution isgenerally called a non-aqueous secondary battery.

The separator is disposed between the positive electrode and thenegative electrode. As the separator, a separator having a separatorsubstrate and a functional layer for a non-aqueous secondary batteryformed on the separator substrate is known (for example, see PatentLiteratures 1 and 2). This functional layer for a non-aqueous secondarybattery may contain a particulate polymer having adhesiveness. Thefunctional layer for a non-aqueous secondary battery may be formed usinga composition for non-aqueous battery functional layers which containssuch a particulate polymer.

The functional layer for a non-aqueous secondary battery may be a layerhaving adhesiveness. When the functional layer for a non-aqueoussecondary battery having adhesiveness is placed between the separatorsubstrate and the electrode (the positive electrode, the negativeelectrode, or both), the adhesion between the separator substrate andthe electrode can be achieved.

CITATION LIST Patent Literature

Patent Literature 1: International Publication No. 2015/145967(corresponding publication: specification of U.S. Patent ApplicationPublication No. 2016/351873)

Patent Literature 2: Japanese Patent Application Laid-Open No.2008-210686 A (corresponding publication: specification of U.S. PatentApplication Publication No. 2008/206645)

SUMMARY Technical Problem

However, the non-aqueous secondary battery is demanded to have furtherimproved performance. Therefore, further improvement of the adhesivenessof the functional layer is demanded.

Also, when the function of the functional layer for a non-aqueoussecondary battery is high, liquid supply to the electrode, that is,distribution of the electrolytic solution to the electrode inside thesecondary battery, can become insufficient, which contrarily reducesbattery performance. For example, life properties (life in repeateduses) may decrease, and/or low-temperature output properties (propertiesof being capable of outputting voltages closer to normal temperatureeven at low temperatures) may decrease.

Furthermore, when a functional layer containing the particulate polymeris used as the functional layer for a non-aqueous secondary battery,blocking of the functional layer for a non-aqueous secondary batteryoccurs, and handling becomes difficult in some cases.

To address this concern, an object of the present invention is toprovide: a functional layer for a non-aqueous secondary battery whichcan express high adhesiveness, provide a non-aqueous secondary batterybeing excellent in performance such as life properties andlow-temperature output properties, and have a facilitated handleability;a composition for a non-aqueous secondary battery functional layer whichenables formation of such a functional layer for a non-aqueous secondarybattery; and a non-aqueous secondary battery including the functionallayer for a non-aqueous secondary battery and having improvedperformance such as life properties and low-temperature outputproperties.

Solution to Problem

The present inventor conducted extensive studies for the purpose ofsolving the aforementioned problem. As a result, the present inventorhas found that when a particulate polymer constituting the compositionfor a non-aqueous secondary battery functional layer is adjusted so asto contain specific monomer units at a specific range of ratios and havea specific range of particle diameters and a specific swelling degree,the performance of the non-aqueous secondary battery can be improvedwhile the adhesiveness of the functional layer for a non-aqueoussecondary battery is enhanced, and furthermore, blocking of thefunctional layer for a non-aqueous secondary battery can be suppressed.The present invention has been achieved on the basis of such knowledge.

That is, the present invention is as follows.

(1) A composition for a non-aqueous secondary battery functional layercomprising a particulate polymer, wherein

the particulate polymer is a copolymer containing

-   -   20% by weight or more and 80% by weight or less of an aromatic        monovinyl monomer unit; and    -   0.01% by weight or more and 2% by weight or less of a polyvalent        ethylenically unsaturated crosslinkable monomer unit,

a volume-average particle diameter D of the particulate polymer is 0.5μm or more and 5 μm or less, and

a swelling degree of the particulate polymer to an electrolyte solutionis more than 1 time and 3 times or less.

(2) The composition for a non-aqueous secondary battery functional layeraccording to (1), wherein an elution amount of the particulate polymerto the electrolyte solution is 0.01% by weight or more and 10% by weightor less.

(3) The composition for a non-aqueous secondary battery functional layeraccording to (1) or (2), further comprising inorganic particles.

(4) A functional layer for a non-aqueous secondary battery formed usingthe composition for a non-aqueous secondary battery functional layeraccording to any one of (1) to (3).

(5) A non-aqueous secondary battery comprising a positive electrode, anegative electrode, a separator, and an electrolyte, wherein

one or more of the positive electrode, the negative electrode, and theseparator have the functional layer for a non-aqueous secondary batteryaccording to (4).

(6) A functional layer for a non-aqueous secondary battery comprising aparticulate polymer, wherein

the particulate polymer is a copolymer containing

-   -   20% by weight or more and 80% by weight or less of an aromatic        monovinyl monomer unit; and    -   0.01% by weight or more and 2% by weight or less of a polyvalent        ethylenically unsaturated crosslinkable monomer unit,

a volume-average particle diameter of the particulate polymer is 0.5 μmor more and 5 μm or less, and

a swelling degree of the particulate polymer to a specific electrolytesolution is more than 1 time and 3 times or less.

Advantageous Effects of the Invention

According to the present invention, a functional layer for a non-aqueoussecondary battery which can express high adhesiveness, provide anon-aqueous secondary battery being excellent in performance such aslife properties and low-temperature output properties, and have afacilitated handleability; a composition for a non-aqueous secondarybattery functional layer which enables formation of such a functionallayer for a non-aqueous secondary battery; and a non-aqueous secondarybattery including the functional layer for a non-aqueous secondarybattery and having improved performance such as life properties andlow-temperature output properties can be provided.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention will be described in detail withreference to embodiments and examples. However, the present invention isnot limited to the following embodiments and examples, and may be freelymodified for implementation without departing from the scope of claimsof the present invention and the scope of their equivalents.

In the present application, the expression “(meth)acryl-” means“acryl-”, “methacryl-” or a combination of these. For example,(meth)acrylic acid means acrylic acid, methacrylic acid, or acombination of these. In addition, (meth)acrylate means acrylate,methacrylate, or a combination of these. Further, (meth)acrylonitrilemeans acrylonitrile, methacrylonitrile, or a combination of these.

In the present application, the term “monomer unit” refers to astructural unit having a structure formed by certain polymerization. Forexample, a (meth)acrylic acid ester monomer unit refers to a structuralunit having a structure formed by polymerizing a (meth)acrylic acidester monomer. A (meth)acrylonitrile monomer unit refers to a structuralunit having a structure formed by polymerizing (meth) acrylonitrile.

[1. Composition for Non-Aqueous Secondary Battery Functional Layer]

The composition for a non-aqueous secondary battery functional layerincludes a specific particulate polymer.

[1.1. Particulate Polymer]

The particulate polymer is a polymer having a particulate shape. Theparticulate polymer can maintain the particulate shape in a compositionfor a functional layer and in a functional layer formed using thecomposition for a functional layer.

The particulate polymer is a copolymer containing an aromatic monovinylmonomer unit and a polyvalent ethylenically unsaturated crosslinkablemonomer unit. The structure of such a copolymer is not particularlylimited. The copolymer may be any of a block copolymer, a graftcopolymer, and a random copolymer, but is preferably a random copolymer.

[1.2. Aromatic Monovinyl Monomer Unit]

Examples of the aromatic monovinyl monomer capable of forming thearomatic monovinyl monomer unit may include styrene, styrenesulfonicacid and salts thereof (for example, sodium styrenesulfonate),α-methylstyrene, vinyltoluene, and 4-(tert-butoxy)styrene. Among these,styrene and sodium styrenesulfonate are preferable, and styrene is morepreferable. One type of these may be solely used, and two or more typesthereof may also be used in combination at any ratio.

The content ratio of the aromatic monovinyl monomer unit in theparticulate polymer is preferably 20% by weight or more, more preferably40% by weight or more, and further preferably 60% by weight or more, andis preferably 80% by weight or less, more preferably 77% by weight orless, further preferably 75% by weight or less. When the content ratioof the aromatic monovinyl monomer unit in the particulate polymer isequal to or more than the aforementioned lower limit value, the elutionamount of the particulate polymer into the electrolyte solution can bereduced, thereby making the low-temperature properties of thenon-aqueous secondary battery excellent.

Furthermore, strength of the particulate polymer can be expressed,thereby enabling suppression of blocking of the functional layer whileenhancing the adhesion. When the content ratio of the aromatic monovinylmonomer unit in the particulate polymer is equal to or less than theaforementioned upper limit value, adhesiveness by the particulatepolymer can be expressed.

[1.3. Polyvalent Ethylenically Unsaturated Crosslinkable Monomer Unit]

The polyvalent ethylenically unsaturated crosslinkable monomer capableof forming the polyvalent ethylenically unsaturated crosslinkablemonomer unit may be a compound having two or more ethylenicallyunsaturated bonds. Examples of the polyvalent ethylenically unsaturatedcrosslinkable monomer may include polyfunctional (meth)acrylates such asallyl (meth)acrylate, ethylene glycol di(meth)acrylate, diethyleneglycol di(meth)acrylate, triethylene glycol di(meth)acrylate,tetraethylene glycol di(meth)acrylate, and trimethylolpropane-tri(meth)acrylate; polyfunctional allyl/vinyl ethers such asdipropylene glycol diallyl ether, polyglycol diallyl ether, triethyleneglycol divinyl ether, hydroquinone diallyl ether, andtetraallyloxyethane; and divinylbenzene. Among these, ethylene glycoldi(meth)acrylate and allyl (meth)acrylate are preferable, and ethyleneglycol di(meth)acrylate is more preferable. One type of these may besolely used, and two or more types thereof may also be used incombination at any ratio.

The content ratio of the polyvalent ethylenically unsaturatedcrosslinkable monomer unit in the particulate polymer is preferably0.01% by weight or more, more preferably 0.05% by weight or more, andfurther preferably 0.1% by weight or more, and is preferably 2% byweight or less, more preferably 1.5% by weight or less, furtherpreferably 1% by weight or less. When the content ratio of thepolyvalent ethylenically unsaturated crosslinkable monomer unit in theparticulate polymer is equal to or more than the aforementioned lowerlimit value, the elution amount of the particulate polymer into theelectrolyte solution can be reduced, whereby the low-temperatureproperties of the non-aqueous secondary battery can be made excellent.Furthermore, strength of the particulate polymer can be expressed,thereby enabling suppression of the blocking of the functional layerwhile enhancing the adhesion. When the content ratio of the polyvalentethylenically unsaturated crosslinkable monomer unit in the particulatepolymer is equal to or less than the aforementioned upper limit value,adhesiveness by the particulate polymer can be expressed.

[Other Monomer Units]

The particulate polymer may contain an optional unit in addition to thearomatic monovinyl monomer unit and the polyvalent ethylenicallyunsaturated crosslinkable monomer unit. Examples of the optional monomermay include a (meth)acrylic acid alkyl ester monomer unit and an acidicgroup-containing monomer unit.

As the (meth)acrylic acid alkyl ester monomer capable of forming the(meth)acrylic acid alkyl ester monomer unit, a (meth)acrylic acid alkylester monomer having one polymerizable unsaturated group per moleculemay be used. Examples of the (meth)acrylic acid alkyl ester monomer mayinclude acrylic acid alkyl esters such as methyl acrylate, ethylacrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate,t-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isopentylacrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexylacrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecylacrylate, and stearyl acrylate; and methacrylic acid alkyl esters suchas methyl methacrylate, ethyl methacrylate, n-propyl methacrylate,isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate,isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate,hexyl methacrylate, heptyl methacrylate, octyl methacrylate,2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate,lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate,and glycidyl methacrylate. Among these, from the viewpoint of enhancingadhesiveness of the functional layer for a non-aqueous secondary batterybefore and after immersion in an electrolyte solution and improving thelife properties of the non-aqueous secondary battery, methylmethacrylate, 2-ethylhexyl acrylate, ethyl acrylate, and butyl acrylateare preferable, and methyl methacrylate and butyl acrylate are morepreferable. With such monomers, desired properties can be imparted tothe particulate polymer. As the (meth)acrylic acid alkyl ester monomer,one type thereof may be solely used, and two or more types thereof mayalso be used in combination at any ratio.

The content ratio of the (meth)acrylic acid alkyl ester monomer unit inthe particulate polymer is preferably 5% by weight or more, morepreferably 7% by weight or more, and further preferably 10% by weight ormore, and is preferably 70% by weight or less, more preferably 60% byweight or less, and further preferably 50% by weight or less. When thecontent ratio of the (meth)acrylic acid alkyl ester monomer unit in theparticulate polymer is equal to or more than the aforementioned lowerlimit value, the elution amount of the particulate polymer into theelectrolyte solution can be reduced, whereby the low-temperatureproperties of the non-aqueous secondary battery can be made excellent.On the other hand, when the content ratio of the (meth)acrylic acidalkyl ester monomer unit in the particulate polymer is equal to or lessthan the aforementioned upper limit value, sufficient adhesiveness canbe expressed.

Examples of the acidic group-containing monomer capable of forming theacidic group-containing monomer unit may include a carboxylic acidgroup-containing monomer, a sulfonic acid group-containing monomer, anda phosphoric acid group-containing monomer. Among these, a carboxylicacid group-containing monomer is preferable.

Examples of the carboxylic acid group-containing monomer may include anethylenically unsaturated monocarboxylic acid and derivatives thereof,and an ethylenically unsaturated dicarboxylic acid and acid anhydridesthereof, and derivatives thereof.

Examples of the ethylenically unsaturated monocarboxylic acid mayinclude acrylic acid, methacrylic acid, and crotonic acid. Examples ofthe derivatives of the ethylenically unsaturated monocarboxylic acid mayinclude 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid,β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, andβ-diaminoacrylic acid.

Examples of the ethylenically unsaturated dicarboxylic acid may includemaleic acid, fumaric acid, itaconic acid, and mesaconic acid. Examplesof the acid anhydrides of the ethylenically unsaturated dicarboxylicacid may include maleic anhydride, acrylic anhydride, methyl maleicanhydride, and dimethyl maleic anhydride. Examples of the derivatives ofthe ethylenically unsaturated dicarboxylic acid may include methylmaleicacid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid,dichloromaleic acid, fluoromaleic acid, diphenyl maleate, nonyl maleate,decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkylmaleate.

Among these, from the viewpoint of making the properties of theparticulate polymer favorable, a carboxylic acid group-containingmonomer is preferable as the acidic group-containing monomer. Acrylicacid, methacrylic acid, and itaconic acid are more preferable, acrylicacid and methacrylic acid are further preferable, and methacrylic acidis particularly preferable. As the acidic group-containing monomer, onetype thereof may be solely used, and two or more types thereof may alsobe used in combination at any ratio.

The content ratio of the acidic group-containing monomer unit in theparticulate polymer is preferably 0.1% by weight or more, morepreferably 0.3% by weight or more, and further preferably 0.5% by weightor more, and is preferably 20% by weight or less, more preferably 10% byweight or less, and further preferably 5% by weight or less. When thecontent ratio of the acidic group-containing monomer unit in theparticulate polymer falls within the aforementioned range, theproperties of the particulate polymer can be made favorable.

[1.5. Volume-Average Particle Diameter D of Particulate Polymer]

The volume-average particle diameter D of the particulate polymer ispreferably 0.5 μm or more, and is preferably 5 μm or less, morepreferably 2 μm or less, and further preferably 1.5 μm or less. When thevolume-average particle diameter D is equal to or more than theaforementioned lower limit value, favorable adhesion between thefunctional layer and a layer in contact with the functional layer can beobtained by the particulate polymer exposed on the surface. When thevolume-average particle diameter D is equal to or less than theaforementioned upper limit value, thickness of the functional layer canbe reduced, and furthermore, an increased capacity of the non-aqueoussecondary battery can be achieved.

In the present application, the volume-average particle diameter D is avolume-average particle diameter D50 in a particle size distribution(based on volume). The volume-average particle diameter D50 represents aparticle diameter (median diameter) at a cumulative volume from thesmall diameter side of 50% in a particle size distribution (based onvolume). The particle size distribution may be measured by acommercially available particle size distribution measuring device.Specifically, the particle size distribution may be measured using alaser diffraction type particle diameter distribution measuring devicewhich will be described in Evaluation items of Examples described in thepresent application.

[1.6. Glass Transition Temperature of Particulate Polymer]

It is preferable that the particulate shape of the particulate polymeris at least partly maintained in the preparation of the composition fora functional layer, in the formation of the functional layer using thecomposition for a functional layer, and in the use of the functionallayer in the secondary battery. Therefore, the glass transitiontemperature of the particulate polymer is preferably at a certain levelor higher. Specifically, the glass transition temperature of theparticulate polymer is preferably 20° C. or higher, more preferably 30°C. or higher, and further preferably 35° C. or higher. The upper limitof the glass transition temperature of the particulate polymer is notparticularly limited to, and may be usually 65° C. or lower. In thepresent application, the glass transition temperature may be measured inaccordance with JIS K7121, using a commercially available differentialscanning calorimeter or the like. Specifically, the glass transitiontemperature may be measured by the following procedure. First, thesubject to be measured is molded as a film having a thickness of 1±0.3mm. This film is dried in a hot air oven at 120° C. for 1 hour. Afterthat, the glass transition temperature (° C.) of the dried film as asample is measured in accordance with JIS K7121, at a measurementtemperature of −100° C. to 180° C. and a rate of temperature increase of5° C./min, using a differential scanning calorimeter (DSC6220SII,manufactured by NanoTechnology Inc.).

When the particulate polymer is a random copolymer, the measured glasstransition temperature is determined as one point. On the other hand,when the particulate polymer is a copolymer other than a randomcopolymer, such as a block copolymer or a graft copolymer, the measuredglass transition temperature is indicated by a plurality of values. Whenthe particulate polymer is a random copolymer, the polymer can behomogenized, durability of the particulate polymer against theelectrolyte solution can be enhanced, and dispersibility in thecomposition for a non-aqueous secondary battery functional layer canalso be enhanced.

[1.7. Swelling Degree and Elution Amount of Particulate Polymer toElectrolyte Solution]

It is preferable that the swelling degree of the particulate polymer tothe electrolyte solution is within a specific range. The swelling degreeto the electrolyte solution is the ratio of the weight change of a filmthat has been formed by molding of the particulate polymer, the weightchange being as a result of immersion of the film in a specificelectrolyte solution at 60° C. for 72 hours. The specific measurementmethod of the swelling degree is as follows. That is, about 0.2 g of thedried particulate polymer is pressed for 2 minutes under the pressconditions of 200° C. and 5 MPa to obtain a film. The obtained film iscut into a 1-cm square to have a test piece. The weight W0 of this testpiece is measured. After that, the test piece is immersed in a specificelectrolyte solution at 60° C. for 72 hours. After that, the test pieceis taken out of the electrolyte solution, and the electrolyte solutionon the surface is wiped off. Then, the weight W1 of the test piece ismeasured. From the obtained values of the weights W0 and W1, theswelling degree S (times) of the particulate polymer is calculated fromformula S=W1/W0. As the aforementioned specific electrolyte solution, anon-aqueous electrolyte solution obtained by dissolving a supportingelectrolyte at a concentration of 1 mol/L in a specific mixed solvent isused. As the specific mixed solvent, a mixture of ethylene carbonate(EC), diethyl carbonate (DEC), and vinylene carbonate (VC) with a volumeratio: EC/DEC/VC=68.5/30/1.5 is used. As the supporting electrolyte,LiPF₆ is used.

The swelling degree S of the particulate polymer is more than 1 time,preferably 1.5 times or more, and more preferably 1.75 times or more,and is 3 times or less, preferably 2.5 times or less, and morepreferably 2.25 times or less. The polymer having such a desiredswelling degree may be obtained by appropriately adjusting thecomposition of its monomer units. When the swelling degree S of theparticulate polymer is equal to or less than the aforementioned upperlimit value, elution of the components of the particulate polymer can besuppressed, and battery properties such as low temperature propertiescan be improved. When the swelling degree S of the particulate polymeris equal to or more than the aforementioned lower limit value, theability to supply the electrolyte solution to the electrode can beexerted, and battery properties such as life properties can be improved.

It is preferable that the elution amount of the particulate polymer tothe electrolyte solution is within a specific range. The elution amountto the electrolyte solution refers to an amount of the particulatepolymer eluting to the electrolyte solution as a result of swelling. Theelution amount may be calculated by drying the test piece after theaforementioned measurement of the swelling degree, measuring the dryweight, and comparing the measured dry weight to the weight before theimmersion. The specific measurement method thereof is as follows. Thatis, the test piece after the measurement of the swelling degree iswashed with methanol 5 times, dried, and measured for the weight W2 ofthe test piece after drying. From the values of the weights W0 and W2,the elution amount X (%) is calculated from formula X=(W2/W0)×100.

The elution amount X of the particulate polymer is preferably 0.01% byweight or more, and is preferably 10% by weight or less, more preferably5% by weight or less, and further more preferably 1% by weight or less.When the elution amount X of the particulate polymer is equal to or lessthan the aforementioned upper limit value, low temperature properties ofthe secondary battery can be improved. When the elution amount X of theparticulate polymer is equal to or more than the aforementioned lowerlimit value, coating of the particulate polymer on the electrode mixturelayer can be achieved, and life properties of the secondary battery canbe improved.

[1.8. Content Ratio of Particulate Polymer]

The content ratio of the particulate polymer in 100% by weight of thesolid content of the composition for a functional layer is preferably 3%by weight or more, more preferably 4% by weight or more, andparticularly preferably 5% by weight or more, and is preferably 95% byweight or less, more preferably 90% by weight or less, and particularlypreferably 85% by weight or less. In the present application, the solidcontent of the composition for a functional layer refers to componentsremained in the functional layer after the functional layer has beenformed using the composition for a functional layer through stepsincluding a drying step, and usually comes to be a sum of all thecomponents other than a solvent. When the content ratio of theparticulate polymer falls within the aforementioned range, thecomposition for a functional layer prepared in a slurry state can haveproperties suitable for coating.

[1.9. Preparation of Particulate Polymer]

The particulate polymer may be prepared by copolymerizing the pluralityof types of monomers described above. The ratio of the monomers forpreparing the copolymer may be usually the same as the ratio of themonomer units in the particulate polymer.

The manner of polymerization of the particulate polymer is notparticularly limited. Examples of the polymerization method to be usedmay include a solution polymerization method, a suspensionpolymerization method, a bulk polymerization method, and an emulsionpolymerization method. As the polymerization reaction, additionpolymerization such as ion polymerization, radical polymerization, andliving radical polymerization may be used. Furthermore, as theemulsifier, dispersant, polymerization initiator, and polymerizationauxiliary used for the polymerization, commonly used ones may be used.Using amounts thereof may also be commonly used amounts.

For preparing the particulate polymer as a random copolymer, thepolymerizable monomer in the monomer composition may be in a state of apolymerizable monomer rather than in a state of an oligomer that hasbeen polymerized to some extent, because thereby generation of a blockcopolymer and a graft copolymer can be suppressed.

The volume-average particle diameter D of the particulate polymer may beadjusted by any known method. For example, the volume-average particlediameter D of the particulate polymer may be adjusted by: changing thetype and amount of the emulsifier and the amount of the polymerizationinitiator; changing the reaction conditions of the polymerizationreaction; extracting the particulate polymer having a necessary particlediameter range from the polymer obtained through the polymerizationreaction; or adding an appropriate amount of the monomer in the presenceof seed particles for polymerization.

[1.10. Dispersion Medium]

The composition for a non-aqueous secondary battery functional layer ofthe present invention may contain optional components in addition to theparticulate polymer. For example, the composition for a non-aqueoussecondary battery functional layer of the present invention may containa dispersion medium. When the composition for a non-aqueous secondarybattery functional layer of the present invention contains a dispersionmedium, the composition can have a property of a slurry. Hereinafter,the composition for a non-aqueous secondary battery functional layer ofthe present invention having the property of a slurry may be referred toas a “slurry composition for a functional layer”. In the formation ofthe functional layer using the slurry composition for a functional layerincluding the step of drying, the dispersion medium is volatilized,whereby a functional layer formed of the solid content of the slurrycomposition for a functional layer can be obtained.

As the dispersion medium, any medium which can be volatilized in theformation of the functional layer, has a low tendency to dissolve theparticulate polymer, and can maintain the dispersed state of theparticulate polymer may be used. As the dispersion medium, an aqueousmedium is preferable. An aqueous medium is water or a mixture of waterand a medium other than water. When an aqueous medium is employed as thedispersion medium, environmental load can be reduced, and handling ofthe slurry composition for a functional layer can be facilitated.

Examples of the medium which may be used in combination with water inthe aqueous medium may include a cyclic aliphatic hydrocarbon compoundsuch as cyclopentane and cyclohexane; an aromatic hydrocarbon compoundsuch as toluene and xylene; a ketone compound such as ethyl methylketone and cyclohexanone; an ester compound such as ethyl acetate, butylacetate, γ-butyrolactone, and ε-caprolactone; a nitrile compound such asacetonitrile and propionitrile; an ether compound such astetrahydrofuran and ethylene glycol diethyl ether; an alcohol compoundsuch as methanol, ethanol, isopropanol, ethylene glycol, and ethyleneglycol monomethyl ether; and an amide compound such asN-methylpyrrolidone (NMP) and N,N-dimethylformamide. One type of thesemay be solely used, and two or more types thereof may also be used incombination at any ratio. The amount of the medium other than water ispreferably 5 parts by weight or less relative to 100 parts by weight ofwater.

It is preferable that the amount of the dispersion medium in the slurrycomposition for a functional layer is set so that the solid contentconcentration of the slurry composition for a functional layer fallswithin a desired range. The specific solid content concentration of theslurry composition for a functional layer is preferably 10% by weight ormore, more preferably 15% by weight or more, and further preferably 20%by weight or more, and is preferably 80% by weight or less, morepreferably 75% by weight or less, further more preferably 70% by weightor less, and particularly preferably 65% by weight or less. When thesolid content concentration falls within the aforementioned range, theslurry composition for a functional layer can have properties suitablefor the coating and drying steps.

[1.11. Inorganic Particles]

The composition for a non-aqueous secondary battery functional layer ofthe present invention may contain inorganic particles as an optionalcomponent. The inorganic particles are particles of an inorganiccompound. The inorganic particle does not dissolve in a dispersionmedium that may be contained in the composition for a functional layernor in a non-aqueous electrolyte solution of the non-aqueous secondarybattery, and can maintain its shape even in the dispersion medium andthe non-aqueous electrolyte solution.

The inorganic compound constituting the inorganic particles ispreferably a material which stably exists in the use environment of thenon-aqueous secondary battery and is electrochemically stable. From sucha viewpoint, preferable examples of the inorganic compound may include:oxide particles such as aluminum oxide (alumina), hydrated aluminumoxide (boehmite), silicon oxide, magnesium oxide (magnesia), calciumoxide, titanium oxide (titania), BaTiO₃, ZrO, and alumina-silicacomposite oxide; nitride particles such as aluminum nitride and boronnitride; covalent crystal particles such as silicon and diamond;poorly-soluble ionic crystal particles such as barium sulfate, calciumfluoride, and barium fluoride; and clay fine particles such as talc andmontmorillonite. The inorganic particle may be a particle obtained bysubjecting the particle formed of these materials to a treatment such aselement substitution, a surface treatment, and solid solution formation.

As the inorganic particles, one type thereof may be solely used, and twoor more types thereof may also be used in combination.

[1.12. Volume-Average Particle Diameter of Inorganic Particles>

The volume-average particle diameter of the inorganic particles ispreferably 0.1 μm or more, more preferably 0.20 μm or more, and furthermore preferably 0.30 μm or more, and is preferably 1.0 μm or less, morepreferably 0.90 μm or less, and further more preferably 0.80 μm or less.When the volume-average particle diameter is equal to or more than theaforementioned lower limit value, the inorganic particles can bedispersed into a slurry state in the composition for a non-aqueoussecondary battery functional layer. Also, the binding force betweenparticles can be expressed in the functional layer, and thereby cohesivefracture when release force is applied to the functional layer can besuppressed, and adhesion of the functional layer can be improved. Inaddition, shrinkage when heat is applied to the functional layer can bereduced. When the volume-average particle diameter is equal to or lessthan the aforementioned upper limit value, the film thickness of thefunctional layer can be reduced, and in turn, an increased capacity ofthe non-aqueous secondary battery can be achieved. Also, when thecomposition for a functional layer is prepared in a slurry state,thixotropy can be imparted to the composition for a functional layer. Asa result, floating of the particulate polymer and blocking of thefunctional layer can be suppressed.

As the inorganic particles, a commercially available product having adesired volume-average particle diameter as it is, or a product obtainedby subjecting the commercially available product to a treatment ifnecessary, may be used. Alternatively, the commercially availableproduct may be used after the volume-average particle diameter thereofhas been adjusted to fall within a desired range by operations such asclassification or crushing.

[1.3. Content Ratio of Inorganic Particles>

The content ratio of the inorganic particles in 100% by weight of thesolid content of the composition for a functional layer is preferably40% by weight or more, more preferably 50% by weight or more, andparticularly preferably 60% by weight or more, and is preferably 99% byweight or less, more preferably 98% by weight or less, and particularlypreferably 97% by weight or less. When the content ratio of theinorganic particles falls within the aforementioned range, properties ofporosity can be imparted to the obtained functional layer to therebyrender the functional layer a layer usable as a porous membrane.Furthermore, when the content ratio of the inorganic particles fallswithin the aforementioned range, the composition for a functional layerprepared into a slurry state can have properties suitable for coating.

[1.14. Weight Ratio between Inorganic Particles and Particulate Polymer]

In the composition for a non-aqueous secondary battery functional layerof the present invention, the weight ratio between the inorganicparticles and the particulate polymer may be appropriately adjusted toobtain a composition for a functional layer and functional layer havingdesired properties. The ratio of the inorganic particles in 100% byweight in total of the inorganic particles and the particulate polymeris preferably 50% by weight or more, more preferably 55% by weight ormore, and further more preferably 60% by weight or more, and ispreferably 95% by weight or less, more preferably 90% by weight or less,and further more preferably 85% by weight or less. When the ratio of theinorganic particles in the total of the inorganic particles and theparticulate polymer is equal to or more than the aforementioned lowerlimit value, blocking of the functional layer can be suppressed.Furthermore, there can be obtained a functional layer which is favorableboth in the heat shrinkage resistance in a dried state and in the heatshrinkage resistance in the electrolyte solution (suppression of theshrinkage due to heating in the electrolyte solution in a state in whichthe functional layer adheres to another constituent element, theadhesion being effected by the conditions for pressing constituentelements such as an electrode and a separator during the production of asecondary battery). When the ratio of the inorganic particles in thetotal of the inorganic particles and the particulate polymer is equal toor less than the aforementioned upper limit value, the relative ratio ofthe particulate polymer can be increased, and as a result reliableadhesion of the functional layer to the electrode can be achieved.

[1.15. Binder for Functional Layer]

The composition for a non-aqueous secondary battery functional layer ofthe present invention may contain a binder for a functional layer as anoptional component. The binder for a functional layer may be a binderhaving an ability to bind the components constituting the functionallayer for a non-aqueous secondary battery to each other, in particular,an ability to bind the above-mentioned inorganic particles to each otherand an ability to bind the inorganic particles and the particulatepolymer to each other.

It is preferable that the glass transition temperature of the binder fora functional layer is lower than a certain level. Specifically, theglass transition temperature of the binder for a functional layer ispreferably 10° C. or lower, more preferably 0° C. or lower, and furtherpreferably −5° C. or lower. The lower limit of the glass transitiontemperature of the binder for a functional layer is not particularlylimited, and may be usually −80° C. or higher. When the binder for afunctional layer has such a low glass transition temperature, the binderfor a functional layer melts in the step of producing the functionallayer using the composition for a functional layer, so that the functionof binding can be satisfactorily expressed.

As the binder for a functional layer, a polymer having desiredproperties may be used. Such a polymer may be a homopolymer composed ofone type of a polymerization unit, and may also be a copolymercontaining two or more types of polymerization units. From the viewpointof adjusting properties such as the particle diameter, glass transitiontemperature, and ability as a binder to desired ranges, it is preferablethat the binder is a copolymer.

As a particularly preferable aspect, the binder for a functional layermay contain a (meth)acrylic acid alkyl ester monomer unit. Examples ofthe (meth)acrylic acid alkyl ester monomer corresponding to the(meth)acrylic acid alkyl ester monomer unit may include acrylic acidalkyl esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate,isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate,hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate,nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate,and stearyl acrylate; and methacrylic acid alkyl esters such as methylmethacrylate, ethyl methacrylate, n-propyl methacrylate, isopropylmethacrylate, n-butyl methacrylate, t-butyl methacrylate, pentylmethacrylate, hexyl methacrylate, heptyl methacrylate, octylmethacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decylmethacrylate, lauryl methacrylate, n-tetradecyl methacrylate, andstearyl methacrylate. One type of these may be solely used, and two ormore types thereof may also be used in combination at any ratio. Amongthese, n-butyl acrylate and 2-ethylhexyl acrylate are preferable fromthe viewpoint of excellent flexibility.

The ratio of the (meth)acrylic acid alkyl ester monomer unit in thebinder for a functional layer is preferably 50% by weight or more, morepreferably 70% by weight or more, and particularly preferably 90% byweight or more, and is preferably 99% by weight or less, more preferably98% by weight or less, and particularly preferably 97% by weight orless. When the ratio of the (meth)acrylic acid ester monomer unit isequal to or more than the aforementioned lower limit value, flexibilityof the functional layer can be enhanced and adhesiveness of thefunctional layer can be enhanced. When the ratio of the (meth)acrylicacid alkyl ester monomer unit is equal to or less than theaforementioned upper limit value, rigidity of the functional layer canbe enhanced, and adhesiveness of the functional layer can also bethereby enhanced.

The binder for a functional layer may contain an acidic group-containingmonomer unit. As the acidic group-containing monomer unit, for example,those selected from the same range as those described as the usableunits in the particulate polymer may be used. As the acidicgroup-containing monomer unit, one type thereof may be solely used, andtwo or more types thereof may also be used in combination at any ratio.

The ratio of the acidic group-containing monomer unit in the binder fora functional layer is preferably 0.2% by weight or more, more preferably0.4% by weight or more, and particularly preferably 0.6% by weight ormore, and is preferably 10.0% by weight or less, more preferably 6.0% byweight or less, and particularly preferably 4.0% by weight or less. Whenthe ratio of the acidic group-containing monomer unit falls within theaforementioned range, cohesive fracture of the functional layer can besuppressed, and adhesiveness of the functional layer in the electrolytesolution can be improved.

In addition, the binder for a functional layer may contain a(meth)acrylonitrile monomer unit. When the binder contains the(meth)acrylonitrile monomer unit, the (meth)acrylonitrile monomercorresponding thereto for use may be acrylonitrile, may bemethacrylonitrile, and may also be a combination of acrylonitrile andmethacrylonitrile.

The ratio of the (meth)acrylonitrile monomer unit in the binder for afunctional layer is preferably 0.2% by weight or more, more preferably0.5% by weight or more, and particularly preferably 1.0% by weight ormore, and is preferably 20.0% by weight or less, more preferably 10.0%by weight or less, and particularly preferably 5.0% by weight or less.When the ratio of the (meth)acrylonitrile monomer unit is equal to ormore than the aforementioned lower limit value, the life of thenon-aqueous secondary battery can be particularly extended. When theratio of the (meth)acrylonitrile monomer unit is equal to or less thanthe aforementioned upper limit value, mechanical strength of thefunctional layer can be increased.

The binder for a functional layer may contain a crosslinkable monomerunit. Examples of the crosslinkable monomer corresponding to thecrosslinkable monomer unit may include the same examples as thoseexemplified as the examples of the polyvalent ethylenically unsaturatedcrosslinkable monomers and the epoxy/N-methylol-based crosslinkablemonomers in the description of the particulate polymer. As thecrosslinkable monomer, one type thereof may be solely used, and two ormore types thereof may also be used in combination at any ratio.

The ratio of the crosslinkable monomer unit in the binder for afunctional layer is preferably 0.2% by weight or more, more preferably0.6% by weight or more, and particularly preferably 1.0% by weight ormore, and is preferably 5.0% by weight or less, more preferably 4.0% byweight or less, and particularly preferably 3.0% by weight or less. Whenthe ratio of the crosslinkable monomer unit is equal to or more than theaforementioned lower limit value, mechanical strength of the functionallayer can be increased. When the ratio thereof is equal to or less thanthe upper limit value, it is possible to prevent flexibility of thefunctional layer from being impaired to become brittle.

The binder for a functional layer may further contain an optionalstructural unit other than the structural units described above.Examples of the optional structural unit may include a structural unithaving a structure formed by polymerizing styrene (styrene unit), and astructural unit having a structure formed by polymerizing butadiene(butadiene unit). As these optional structural units, one type thereofmay be solely used, and two or more types thereof may also be used incombination at any ratio.

In the composition for a functional layer, the binder for a functionallayer may be present in a state of being dissolved in a dispersionmedium, and may also be present having a particulate shape. When thebinder for a functional layer is a particulate polymer, thevolume-average particle diameter of the particles of the binder for afunctional layer is preferably 0.05 μm or more, more preferably 0.1 μmor more, and particularly preferably 0.15 μm or more, and is preferably0.4 μm or less, more preferably 0.35 μm or less, and particularlypreferably 0.3 μm or less. When the volume-average particle diameter ofthe binder for a functional layer is equal to or more than the lowerlimit value of the aforementioned range, dispersibility of the binderfor a functional layer can be enhanced. When the volume-average particlediameter of the binder for a functional layer is equal to or less thanthe upper limit value, binding property of the functional layer can beenhanced. When the composition for a non-aqueous secondary batteryfunctional layer of the present invention contains a particulate polymeras the binder for a functional layer, the volume-average particlediameter of the polymer having the shape of the particles with a glasstransition temperature of 20° C. or higher is adopted as thevolume-average particle diameter D in the composition for a non-aqueoussecondary battery functional layer.

Examples of the method for producing the binder for a functional layermay include a solution polymerization method, a suspensionpolymerization method, and an emulsion polymerization method. Amongthese, an emulsion polymerization method and a suspension polymerizationmethod are preferable because they can be performed in water and theresulting product therefrom as it is can be preferably used as amaterial of the slurry composition for a functional layer. When thebinder for a functional layer is produced, it is preferable that thereaction system contains a dispersant. Usually, the binder for afunctional layer is formed substantially by the polymer constituting thebinder, but may be accompanied by an optional component such asadditives used in the polymerization.

The amount of the binder for a functional layer is preferably 0.1 partby weight or more, and more preferably 0.2 part by weight or more, andis preferably 30 parts by weight or less, and more preferably 25 partsby weight or less, relative to 100 parts by weight of the total of theinorganic particles and the particulate polymer. When the amount of thebinder for a functional layer is equal to or more than the lower limitvalue of the aforementioned range, expansion of a cell of a battery dueto charging and discharging can be suppressed, so that the shape of thecell of the battery can be maintained for a long period of time. Whenthe amount thereof is equal to or less than the upper limit value, alow-temperature output property of the secondary battery can be madefavorable.

[1.16. Other Optional Component]

The composition for a non-aqueous secondary battery functional layer ofthe present invention may contain other optional components in additionto the components described above. The optional component is notparticularly limited as long as it does not excessively giveunpreferable influence to the battery reaction in the secondary batteryusing the functional layer. The types of the optional components may beone type, and may also be two or more types.

Examples of the optional component may include a wetting agent, aleveling agent, an electrolyte decomposition inhibitor, and awater-soluble polymer compound. The water-soluble polymer compound isnot particularly limited, and examples thereof used may include thosedescribed in Japanese Patent Application Laid-Open No. 2014-063754 A.

[1.17. Preparation of Composition for Non-Aqueous Secondary BatteryFunctional Layer]

The method for preparing the composition for a functional layer is notparticularly limited. The composition is usually obtained by mixing theabove-mentioned particulate polymer, and optional components (dispersionmedium, inorganic particles, binder for a functional layer, and otheroptional components) used if necessary. There is no particularlimitation imposed on the mixing method, and mixing is performed using adisperser as a mixing apparatus in order to efficiently disperserespective components.

The disperser is preferably an apparatus capable of uniformly dispersingand mixing the aforementioned components. Examples thereof may include aball mill, a sand mill, a pigment disperser, a crusher, an ultrasonicdisperser, a homogenizer, and a planetary mixer.

[2. Functional Layer for Non-Aqueous Secondary Battery]

The functional layer for a non-aqueous secondary battery of the presentinvention is a layer formed using the composition for a non-aqueoussecondary battery functional layer described above.

The functional layer for a non-aqueous secondary battery of the presentinvention may be formed by, for example, applying the above-mentionedcomposition for a functional layer onto a surface of an appropriatesubstrate to form a coating film, and then drying the formed coatingfilm.

Since the functional layer for a non-aqueous secondary battery of thepresent invention is formed using the composition for a non-aqueoussecondary battery functional layer of the present invention describedabove, excellent adhesiveness can be expressed. Therefore, in the casewhere the functional layer for a non-aqueous secondary battery of thepresent invention is provided as, for example, an adhesive layer forbonding other constituent elements, or a porous membrane for separatingthe positive electrode and the negative electrode, in the non-aqueoussecondary battery, effects such as improvement of low temperature outputproperties and life properties of the non-aqueous secondary battery canbe expressed.

[2.1. Substrate]

Herein, there is no limitation imposed on the substrate onto which thecomposition for a functional layer is applied. For example, a coatingfilm of the composition for a functional layer may be formed on thesurface of a release substrate, the coating film may be dried to form afunctional layer, and the release substrate may be peeled off from thefunctional layer. By doing so, the functional layer peeled off from therelease substrate may be used as an independent film for forming thebattery member of the secondary battery. Specifically, the functionallayer peeled off from the release substrate may be laminated on aseparator substrate to form a separator including the functional layer.Alternatively, the functional layer peeled off from the releasesubstrate may be laminated on an electrode substrate to form anelectrode including the functional layer.

However, from the viewpoint of enhancing the production efficiency ofthe battery member by omitting the step of peeling off the functionallayer, it is preferable to use a separator substrate or an electrodesubstrate as the substrate. The functional layer provided on theseparator substrate and the electrode substrate can suitably function asa protective layer (heat resistant layer) for improving heat resistance,strength, and the like of the separator and the electrode.

[2.2. Separator Substrate]

The separator substrate is not particularly limited, and may be anyseparator substrate such as an organic separator substrate. The organicseparator substrate is a porous member formed of an organic material.Examples of the organic separator substrate may include amicro-functional layer and nonwoven fabric that contain a polyolefinresin such as polyethylene or polypropylene, an aromatic polyamideresin, and the like. A micro-functional layer and nonwoven fabric madeof polyethylene are preferable from the viewpoint of excellent strength.The thickness of the organic separator substrate may be any thickness,and is usually 0.5 μm or more, and preferably 5 μm or more, and isusually 40 μm or less, preferably 35 μm or less, and more preferably 30μm or less.

[2.3. Electrode Substrate]

The electrode substrate (positive electrode substrate and negativeelectrode substrate) is not particularly limited, and may be a substrateincluding a current collector and an electrode mixture layer providedthereon.

Known methods may be adopted as the methods for forming a currentcollector, an electrode active material in an electrode mixture layer(positive electrode active material and negative electrode activematerial) and a binder for the electrode mixture layer (binder for thepositive electrode mixture layer and binder for the negative electrodemixture layer), and an electrode mixture layer formed on the currentcollector. For example, those described in Japanese Patent ApplicationLaid-Open No. 2013-145763 A may be adopted.

[2.4. Method for Forming Functional Layer for Non-Aqueous SecondaryBattery]

As a method for forming a functional layer on a substrate such as aseparator substrate and an electrode substrate, the following method maybe mentioned.

(1) A method of applying the composition for a functional layer onto asurface of a separator substrate or an electrode substrate (in the caseof the electrode substrate, a surface on the electrode mixture layerside, hereinafter the same) and then drying the same;

(2) A method of immersing a separator substrate or an electrodesubstrate in the composition for a functional layer and then drying thesame; and

(3) A method of producing a functional layer by applying the compositionfor a functional layer on a release substrate and drying the same, andtransferring the obtained functional layer to the surface of a separatorsubstrate or an electrode substrate;

Among these, the method (1) is particularly preferable because the filmthickness of the functional layer can be easily controlled. Explainingin more detail, the method (1) includes a step of applying thecomposition for a functional layer onto the substrate (applicationstep), and a step of drying the composition for a functional layerapplied onto the substrate to form the functional layer (drying step).

[2.5. Application Step]

There is no particular limitation imposed on the method for applying thecomposition for a functional layer onto the substrate in the applicationstep. Examples of the application method may include a doctor blademethod, a reverse roll method, a direct roll method, a gravure method,an extrusion method, and a brush coating method.

[2.6. Drying Step]

The method for drying the composition for a functional layer on thesubstrate is not particularly limited, and a known method may be used.Examples of the drying method may include drying by warm air, hot air,or low humidity air, vacuum drying, and a drying method by irradiationwith infrared rays, electron beams, or the like. The drying conditionsare not particularly limited, and the drying temperature is preferably50 to 100° C., and the drying time is preferably 5 to 30 minutes.

[2.7. Thickness of Functional Layer]

The thickness of the functional layer for a non-aqueous secondarybattery of the present invention is preferably 0.01 μm or more, morepreferably 0.1 μm or more, and further preferably 1 μm or more, and ispreferably 20 μm or less, more preferably 10 μm or less, and furtherpreferably 5 μm or less. When the thickness of the functional layer is0.01 μm or more, strength of the functional layer can be sufficientlyensured. When the thickness is 20 μm or less, the diffusivity of theelectrolyte solution can be ensured, and performance of the secondarybattery using the functional layer can be improved.

[2.8. Properties of Functional Layer]

Since the functional layer for a non-aqueous secondary battery of thepresent invention contains a specific particulate polymer, thefunctional layer can be a layer having high adhesiveness. Specifically,adhesion with another constituent element can be easily achieved by theconditions for pressing constituent elements such as an electrode and aseparator during the production of a secondary battery. Morespecifically, when the functional layer for a non-aqueous secondarybattery is provided as a layer on the surface of the separator, astacked body in which the electrode and the separator adhere to eachother to be integrated can be obtained by stacking the electrode and theseparator, and performing pressing under the conditions such as a loadof 10 kN/m and a temperature of 80° C.

Since the functional layer for a non-aqueous secondary battery of thepresent invention contains a specific particulate polymer, thefunctional layer also can be a layer having suppressed blockingproperties while having high adhesiveness as previously described.Specifically, the functional layer for a non-aqueous secondary batterycan reduce the degree of the adhesion of the functional layers after thefunctional layers have been brought into intimate contact with eachother by placing them in the state of being stacked under the conditionsfor storing the functional layers prior to the production of thesecondary battery.

[3. Non-Aqueous Secondary Battery]

The non-aqueous secondary battery of the present invention includes theaforementioned functional layer for a non-aqueous secondary battery ofthe present invention. More specifically, the non-aqueous secondarybattery of the present invention includes a positive electrode, anegative electrode, a separator, and an electrolyte solution. One ormore of the positive electrode, the negative electrode, and theseparator have the aforementioned functional layer for a non-aqueoussecondary battery of the present invention. Since the non-aqueoussecondary battery according to the present invention includes thefunctional layer formed using the composition for a functional layer ofthe present invention, it exerts excellent battery properties such ashigh life properties (life in repeated uses) and high low-temperatureoutput properties (properties of being capable of outputting voltagescloser to normal temperature even at low temperatures).

[3.1. Positive Electrode, Negative Electrode, and Separator]

When the non-aqueous secondary battery of the present inventionincludes, as the separator, a separator having the aforementionedfunctional layer for a non-aqueous secondary battery of the presentinvention, the separator may include a separator substrate and thefunctional layer provided on one or both of the surfaces of theseparator substrate.

When the non-aqueous secondary battery of the present inventionincludes, as the electrode (positive electrode and/or negativeelectrode), an electrode having the aforementioned functional layer fora non-aqueous secondary battery of the present invention, the electrodemay have a current collector, an electrode mixture layer provided on thecurrent collector, and the functional layer provided on the electrodemixture layer. The electrode mixture layer and the functional layer maybe provided on only one surface of the current collector, or may beprovided on both surfaces.

When one of the positive electrode, the negative electrode, and theseparator of the non-aqueous secondary battery of the present inventionhas the aforementioned functional layer for a non-aqueous secondarybattery of the present invention, the others may have the functionallayer for a non-aqueous secondary battery of the present invention, ormay not have the functional layer for a non-aqueous secondary battery ofthe present invention. The electrode which does not have the functionallayer for a non-aqueous secondary battery of the present invention mayinclude, for example, a current collector and an electrode mixture layerprovided on the current collector. The separator which does not have thefunctional layer for a non-aqueous secondary battery of the presentinvention may consist of, for example, a separator substrate.

[3.2. Electrolyte Solution]

The secondary battery of the present invention is a non-aqueoussecondary battery, and therefore, a non-aqueous electrolyte solution isused as the electrolyte solution.

As the non-aqueous electrolyte solution, an organic electrolyte solutionin which a supporting electrolyte is dissolved in an organic solvent isusually used. As the supporting electrolyte, for example, a lithium saltis used in a lithium ion secondary battery. Examples of the lithium saltmay include LiPF₆, LiAsF₆, LiBF₄, LiSbF₆, LiAlCl₄, LiClO₄, CF₃SO₃Li,C₄F₉SO₃Li, CF₃COOLi, (CF₃CO)₂NLi, (CF₃SO₂)₂NLi, and (C₂F₅SO₂)NLi. Amongthese, LiPF₆, LiClO₄, and CF₃SO₃Li are preferable because they can beeasily dissolved in a solvent and exhibits a high degree ofdissociation. As the electrolyte, one type thereof may be solely used,and two or more types thereof may also be used in combination at anyratio. Usually, the higher the dissociation degree of the supportingelectrolyte, the higher the lithium ion conductivity tends to be, sothat the lithium ion conductivity can be adjusted by selecting the typeof the supporting electrolyte.

As the organic solvent used for the electrolyte solution, an organicsolvent capable of dissolving the supporting electrolyte may beappropriately selected. Examples of the organic solvent in a lithium ionsecondary battery may include carbonates such as dimethyl carbonate(DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylenecarbonate (PC), butylene carbonate (BC), and methyl ethyl carbonate(MEC); esters such as γ-butyrolactone and methyl formate; ethers such as1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compoundssuch as sulfolane and dimethylsulfoxide. A mixture of these solvents mayalso be used. Among these, carbonates are preferable because of theirhigh dielectric constant and wide stable electropotential region.Usually, the lower the viscosity of the solvent used, the higher thelithium ion conductivity tends to be, so that the lithium ionconductivity can be adjusted by selecting the type of the solvent.

The concentration of the electrolyte in the electrolyte solution may beadjusted as appropriate. Known additives may also be added to theelectrolyte solution.

[3.3. Shape and Production Method of Non-Aqueous Secondary Battery]

The aforementioned non-aqueous secondary battery of the presentinvention may be produced by, for example, stacking a positive electrodeand a negative electrode via a separator, winding or folding the stackedpositive and negative electrodes if necessary, placing the electrodes ina battery container, and filling the battery container with anelectrolyte solution and sealing the container. At least one memberamong the positive electrode, the negative electrode, and the separatoris a member having the functional layer. Also, expanded metal, anovercurrent prevention element such as a fuse and a PTC element, a leadplate, and the like may be placed in the battery container if necessaryto prevent the pressure increase inside the battery, and theovercharging and overdischarging. The shape of the battery may be any ofcoin-shape, button-shape, sheet-shape, cylindrical, rectangular, flat,and the like.

EXAMPLES

Hereinafter, the present invention will be specifically described byillustrating Examples. However, the present invention is not limited tothe Examples described below. The present invention may be optionallymodified for implementation without departing from the scope of claimsof the present invention and the scope of their equivalents.

In the following description, “%” and “part” representing quantity areon the basis of weight, unless otherwise specified. The operationdescribed below was performed under the conditions of normal temperatureand normal pressure, unless otherwise specified.

[Evaluation Items]

(Volume-Average Particle Diameter D)

The volume-average particle diameter D of the particulate polymer wasmeasured by a laser diffraction method. Specifically, an aqueousdispersion liquid (solid content concentration: 0.1% by weight)containing particles was prepared as a measurement sample, and thevolume-average particle diameter of the particles was measured using alaser diffraction particle diameter distribution measuring device(manufactured by Beckman Coulter, Inc., product name: “LS-230”). Morespecifically, the particle diameter at a cumulative volume from thesmall diameter side of 50% in a particle size distribution (based onvolume) obtained from the measurement result of the laser diffractionparticle diameter distribution measuring device was adopted as thevolume-average particle diameter (μm).

(Swelling Degree)

The aqueous dispersion liquid containing the particulate polymer waspoured in a polytetrafluoroethylene petri dish, and dried under theconditions of 25° C. and 48 hours to prepare a powder. The powder in anamount of about 0.2 g was pressed for 2 minutes under the pressconditions of 200° C. and 5 MPa to obtain a film. The obtained film wascut into a 1-cm square to obtain a test piece. The weight W0 of thistest piece was measured.

After that, the test piece was immersed in a specific electrolytesolution at 60° C. for 72 hours. After that, the test piece was takenout of the electrolyte solution, and the electrolyte solution on thesurface was wiped off. Then, the weight W1 of the test piece wasmeasured.

From the obtained values of the weights W0 and W1, the swelling degree S(times) of the particulate polymer was obtained from formula S=W1/W0.

As the aforementioned specific electrolyte solution, a non-aqueouselectrolyte solution obtained by dissolving a supporting electrolyte ata concentration of 1 mol/L in a specific mixed solvent was used. As thespecific mixed solvent, a mixture of ethylene carbonate (EC), diethylcarbonate (DEC), and vinylene carbonate (VC) with a volume ratio:EC/DEC/VC=68.5/30/1.5 was used. As the supporting electrolyte, LiPF6 wasused.

(Elution Amount)

The test piece after the measurement of swelling degree was washed withmethanol 5 times, and then dried. The weight W2 of the test piece afterthe drying was measured.

From the values of the obtained weights W0 and W2, the elution amount X(%) was obtained from formula X=(W2/W0)×100.

(Glass Transition Temperatures of Binder for Functional Layer andParticulate Polymer)

The aqueous dispersion liquid containing the binder for a functionallayer and the aqueous dispersion liquid containing the particulatepolymer were each dried in the environment of a humidity of 50% and atemperature of 23 to 25° C. for 3 days to obtain a film having athickness of 1±0.3 mm. This film was dried in a hot air oven at 120° C.for 1 hour. The glass transition temperature (° C.) of this dried filmas a sample was measured in accordance with JIS K7121 at a measurementtemperature of −100° C. to 180° C. and a rate of temperature increase of5° C./min, using a differential scanning calorimeter (DSC6220SII,manufactured by NanoTechnology Inc.).

(Adhesiveness of Functional Layer for Non-Aqueous Secondary Battery)

The electrodes and separators obtained in Examples and ComparativeExamples were each cut out to have a cut piece of 10 mm in width×50 mmin length. As the electrode, the positive electrode was cut out inExample 14, and the negative electrode was cut out in other Examples andComparative Examples.

The cut piece of the electrode and the cut piece of the separator werestacked. In Example 14, the cut piece of the separator was stacked onthe cut piece of the positive electrode in such a manner that theseparator substrate-side surface thereof (the surface on the sidewithout a porous membrane) is brought into contact with the cut piece ofthe positive electrode. In Example 15, the cut piece of the separatorwas stacked on the cut piece of the negative electrode in such a mannerthat the separator substrate-side surface thereof is brought intocontact with the cut piece of the negative electrode.

The cut pieces, which were stacked, were pressed using a roll pressunder the conditions of a load of 10 kN/m and a temperature of 80° C. toobtain a test piece in which the cut piece of the electrode and the cutpiece of the separator were integrated.

A cellophane tape was fixed on a horizontal test board with the adhesivesurface thereof facing upward. As the cellophane tape in this operation,a cellophane tape defined in JIS 21522 was used. The obtained test piecewas bonded to the cellophane tape with the electrode-side surface of thetest piece facing downward. Then, one end of the separator side of thetest piece was pulled toward the vertical direction at a speed of 50mm/min for peeling. The stress at that time was measured. The samemeasurement was performed three times, and the average value of themeasurement results was obtained as the peel strength. On the basis ofthe value of the obtained peel strength, the adhesiveness was determinedin accordance with the following criteria. A larger value of the peelstrength is indicative of higher adhesiveness of the functional layerfor a non-aqueous secondary battery.

A: Peel strength is 20 N/m or more.

B: Peel strength is 15 N/m or more and less than 20 N/m.

C: Peel strength is less than 15 N/m.

(Blocking Property)

The separator or electrode obtained in Examples and Comparative Exampleswas cut out to have square cut pieces of 5 cm in width×5 cm in length.As the separator and electrode, a positive electrode was cut out inExample 14, a negative electrode was cut out in Example 15, andseparators were cut out in other Examples and Comparative Examples.

Two cut pieces were stacked, and subjected to the pressurizationconditions of 40° C. and 10 g/cm² for 5 minutes to prepare a measurementsample.

The obtained measurement sample was left to stand for 24 hours, and thenmeasured for blocking strength. Specifically, after the measurementsample was cut into a strip of 2 cm×5 cm, one of the two cut pieces washorizontally fixed, and the other was pulled toward the verticaldirection at a speed of 50 mm/min for peeling. The stress at that timewas measured. The same measurement was performed three times, and theaverage value of the measurement results was obtained as the blockingstrength. On the basis of the value of the obtained blocking strength,the blocking property was determined in accordance with the followingcriteria.

A: No adhesion occurred after having been left to stand for 24 hours.

B: Blocking strength is more than 0 N/m and less than 0.25 N/m.

C: Blocking strength is 0.25 N/m or more.

(Low-Temperature Output Properties)

The 800 mAh wound type lithium ion secondary batteries produced inExamples and Comparative Examples were left to stand in the environmentof 25° C. for 24 hours. Thereafter, charging was performed at a chargingrate of 0.1 C for 5 hours in the environment of 25° C. After thecharging was completed, the voltage V₀ was measured.

Subsequently, discharging was performed at a discharging rate of 1 C inthe environment of −10° C. After 15 seconds from the initiation of thedischarging, the voltage V₁ was measured. Then, the voltage change ΔVwas calculated from formula ΔV=V₀−V₁.

On the basis of the value of the voltage change ΔV obtained by thecalculation, the low-temperature output properties of the non-aqueoussecondary battery was determined in accordance with the followingcriteria. A smaller value of the voltage change ΔV is indicative ofbetter low-temperature output properties of the non-aqueous secondarybattery.

A: Voltage change ΔV is less than 100 mV.

B: Voltage change ΔV is 100 mV or more and less than 200 mV.

C: Voltage change ΔV is 200 mV or more.

(Life Properties)

The 800 mAh non-aqueous secondary batteries produced in Examples andComparative Examples were charged up to 4.2 V with a constant current of800 mA, and then charged with a constant voltage of 4.2 V until thecurrent value reached 20 mA, in 25° C. environment. After that,discharging was performed down to 3.0 V with a constant current of 800mA in 25° C. environment. This charging and discharging was repeateduntil the discharge capacity reached 640 mAh. This time point wasadopted as the lifetime of the battery. Evaluation was performed on fivescales from A to E. A higher number of charging and discharging isindicative of better life properties.

A: 500 times or more

B: 450 times or more and less than 500 times

C: 400 times or more and less than 450 times

D: 300 times or more and less than 400 times

E: less than 300 times

Example 1

(1-1. Preparation of Aqueous Dispersion Liquid Containing Binder forFunctional Layer)

Into a reaction vessel equipped with a stirrer, 70 parts of ionexchanged water, 0.15 part of sodium lauryl sulfate (Kao Chemicals,product name “EMAL 2F”) as an emulsifier, and 0.5 part of ammoniumpersulfate as a polymerization initiator were each supplied.Subsequently, the gas phase inside the reaction vessel was substitutedwith nitrogen gas, and the temperature of the liquid phase inside thereaction vessel was increased to 60° C.

Into another container, 50 parts of ion exchanged water; 0.5 part ofsodium dodecylbenzenesulfonate as an emulsifier; and 94 parts of n-butylacrylate, 2 parts of acrylonitrile, 2 parts of methacrylic acid, 1 partof N-hydroxymethylacrylamide, and 1 part of allyl glycidyl ether aspolymerizable monomers were supplied and mixed, whereby a monomermixture was obtained.

The obtained monomer mixture was continuously supplied into the reactionvessel over 4 hours for performing polymerization. While the monomermixture was supplied, the temperature inside the reaction vessel wasmaintained at 60° C. After the supply of the monomer mixture wasfinished, the temperature was elevated to 70° C., and stirring wascontinued over another 3 hours. After that, the polymerization reactionwas terminated. As a result, an aqueous dispersion liquid containing anacryl-based polymer as a binder for a functional layer was prepared. Theglass transition temperature of the binder for a functional layer wasmeasured. The result was −11° C.

(1-2. Preparation of Particulate Polymer for Functional Layer)

Into a 5 MPa pressure resistant container equipped with a stirrer, amonomer composition, 1 part of sodium dodecylbenzenesulfonate as anemulsifier, 150 parts of ion exchanged water, and 0.5 part of potassiumpersulfate as a polymerization initiator were charged. The mixture wassufficiently stirred, and then warmed to 60° C. The monomer compositionwas prepared as a composition containing 75 parts of styrene (St), 20parts of n-butyl acrylate (BA), 4 parts of methacrylic acid (MAA), and 1part of ethylene glycol dimethacrylate (EDMA). In this manner, thepolymerization of the polymerizable monomers was initiated. At the timepoint when the polymerization conversion rate reached 96%, the reactionmedium was cooled to stop the polymerization reaction. As a result, anaqueous dispersion liquid containing a particulate polymer was prepared.

The volume-average particle diameter D, swelling degree S, and elutionamount X of the obtained particulate polymer were measured. Also, theglass transition temperature of the particulate polymer was measured.The result was 60° C.

(1-3. Preparation of Slurry Composition for Functional Layer)

Using a ball mill, 80 parts by weight in terms of solid content ofalumina (manufactured by Sumitomo Chemical Co., Ltd., product name“AKP3000”, volume-average particle diameter: 0.5 μm, density: 3.9 g/cm³)as inorganic particles; 20 parts by weight in terms of solid content ofthe aqueous dispersion liquid of the particulate polymer obtained in(1-2); 5 parts by weight in terms of solid content of the aqueousdispersion liquid of the binder for a functional layer obtained in(1-1); 1.5 parts by weight of polyacrylamide (PAAm) as a thickener; 0.8part by weight of sodium polyacrylate (product name: Aqualic GL366,manufactured by Nippon Shokubai Co., Ltd.) as a dispersant; and ionexchanged water in such an amount that the solid content concentrationin the reaction medium becomes 40% were mixed. As a result, a slurrycomposition for a functional layer was prepared.

(1-4. Production of Separator)

A separator substrate composed of three layers that arepolypropylene/polyethylene/polypropylene (separator thickness: 25 μm,product name “Celgard 2325”) was prepared as a separator substrate. Ontoone surface of this separator substrate, the slurry composition for afunctional layer obtained in (1-3) was applied such that the thicknessof the coating film became 2 μm. After that, the coating film was driedat 50° C. for 10 minutes. Thus, a functional layer for a non-aqueoussecondary battery was formed on one surface of the separator substrate.Subsequently, another functional layer for a non-aqueous secondarybattery was formed also on the other surface of the separator substrateby the same operation as the aforementioned operation. Accordingly, aseparator including the separator substrate and the functional layersfor a non-aqueous secondary battery disposed on both surfaces of theseparator substrate was obtained. The thickness of the functional layerof each layer in the obtained separator was 2 μm. The obtained separatorwas evaluated for blocking properties.

(1-5. Production of Negative Electrode: Preparation of Binder forNegative Electrode)

A mixed liquid of: 61.5 parts of styrene, 35 parts of 1,3-butadiene, and3.5 parts of itaconic acid as polymerizable monomers; 0.25 part oft-dodecyl mercaptan as a chain transfer agent; and 0.35 part of sodiumlauryl sulfate as an emulsifier was prepared. The mixed liquid wassupplied from a container containing the mixed liquid to a pressureresistant container. Simultaneously with the supply, 1 part of potassiumpersulfate as a polymerization initiator was added into the pressureresistant container. As a result, the polymerization reaction of thepolymerizable monomers was initiated. The temperature during thepolymerization reaction was maintained at 75° C.

After 5.5 hours from the initiation of the polymerization, addition ofthe entire amount of the aforementioned polymerizable monomers wascompleted. Subsequently, the reaction system was warmed to 85° C. tocontinue the polymerization reaction. At the time point when thepolymerization conversion rate reached 97% (after 6 hours from theinitiation of the polymerization reaction at 85° C.), the reactionmedium was cooled to stop the reaction. As a result, a mixturecontaining a particulate polymer was obtained. To the obtained mixturecontaining the particulate polymer, a 5% aqueous sodium hydroxidesolution was added to adjust the pH of the mixture to 8. After that,distillation by heat and reduced pressure was performed to removeunreacted monomers. After that, the mixture was cooled, whereby anaqueous dispersion liquid (solid content concentration: 40%) containinga styrene-butadiene copolymer as a binder for a negative electrode wasobtained.

(1-6. Production of Negative Electrode: Preparation of SlurryComposition for Negative Electrode)

97 parts of artificial graphite (volume-average particle diameter: 15.6μm) as a negative electrode active material and 1 part in terms of solidcontent of a 2% aqueous solution of sodium carboxymethyl cellulose salt(manufactured by Nippon Paper Industries Co., Ltd., product name“MAC350HC”) as a thickener were mixed. To the mixture, ion exchangedwater was added to adjust the solid content concentration to 68%. Afterthat, the obtained product was stirred at a temperature of 25° C. for 60minutes to obtain a mixed liquid. To the obtained mixed liquid, ionexchanged water was further added to adjust the solid contentconcentration to 62%. After that, the obtained product was stirred at atemperature of 25° C. for 15 minutes.

To the mixed liquid, 2 parts in terms of solid content of the aqueousdispersion liquid containing a binder for a negative electrode obtainedin (1-5) was added, and ion exchanged water was added to obtain a finalsolid content concentration of 52%. The obtained product wascontinuously stirred for 10 minutes to obtain a polymer mixed liquid.The polymer mixed liquid was subjected to a defoaming treatment underreduced pressure to obtain a slurry composition for a negativeelectrode.

(1-7. Production of Negative Electrode: Formation of Negative ElectrodeMixture Layer)

The slurry composition for a negative electrode obtained in (1-6) wasapplied onto one surface of a copper foil (thickness: 20 μm) as acurrent collector for a negative electrode using a comma coater suchthat the film thickness after drying became about 150 μm. Subsequently,the copper foil coated with the slurry composition for a negativeelectrode was conveyed at a speed of 0.5 m/min in an oven at 60° C. over2 minutes, so that the slurry composition for a negative electrode wasdried. After that, the copper foil coated with the slurry compositionfor a negative electrode was subjected to a heating treatment at atemperature of 120° C. for 2 minutes. As a result, a negative electrodemixture layer was formed on one surface of the current collector for anegative electrode. Subsequently, the same operation was performed alsoto the other surface of the current collector for a negative electrodeto obtain a primary negative electrode containing the current collectorfor a negative electrode and the negative electrode mixture layerprovided on both surfaces of the current collector for a negativeelectrode. The primary negative electrode was rolled by a roll press tothereby obtain a negative electrode in which each of the negativeelectrode mixture layers on both sides has a thickness of 80 μm. Theobtained negative electrode and the separator obtained in (1-4) wereevaluated for the adhesiveness of the separator to the electrode.

(1-8. Production of Positive Electrode: Preparation of SlurryComposition for Positive Electrode)

94 parts of NMC (LiNi_(0.8)Co_(0.1)Mn_(0.1)O₂, volume-average particlediameter: 10 μm) as a positive electrode active material; 3 parts ofacetylene black (manufactured by Denki Kagaku Kogyo Kabushiki Kaisha,product name “HS-100”) as an electroconductive material; and 3 parts interms of solid content of polyvinylidene fluoride (manufactured byKureha Corporation, product name “#7208”) as a binder for a positiveelectrode were mixed. To the mixture, N-methylpyrrolidone was added as asolvent to obtain a mixed liquid in which the total solid contentconcentration was adjusted to 70%. The mixed liquid was mixed by aplanetary mixer, whereby a slurry composition for a positive electrodewas obtained.

(1-9. Production of Positive Electrode: Formation of Positive ElectrodeMixture Layer)

The slurry composition for a positive electrode obtained in (1-8) wasapplied onto one surface of an aluminum foil (thickness: 20 μm) as acurrent collector for a positive electrode using a comma coater suchthat the film thickness after drying became about 150 μm. Subsequently,the aluminum foil coated with the slurry composition for a positiveelectrode was conveyed at a speed of 0.5 m/min in an oven at 60° C. over2 minutes, so that the slurry composition for a positive electrode wasdried. After that, the aluminum foil coated with the slurry compositionfor a positive electrode was subjected to a heating treatment at atemperature of 120° C. for 2 minutes. As a result, a positive electrodemixture layer was formed on one surface of the current collector for apositive electrode. Subsequently, the same operation was performed alsoto the other surface of the current collector for a positive electrodeto obtain a primary positive electrode containing the current collectorfor a positive electrode and the positive electrode mixture layerprovided on both surfaces of the current collector for a positiveelectrode. The primary positive electrode was rolled by a roll press tothereby obtain a positive electrode in which each of the positiveelectrode mixture layers on both sides has a thickness of 60 μm.

(1-10. Production of Non-Aqueous Secondary Battery)

The positive electrode obtained in (1-9) was cut out to obtain arectangular positive electrode of 49 cm×5.0 cm. The separator obtainedin (1-4) was cut out to obtain two rectangular separators of 55 cm×5.5cm. Also, the negative electrode obtained in (1-7) was cut out to obtaina rectangular negative electrode of 50 cm×5.2 cm.

These were stacked to obtain a stacked body having the layer structureof (rectangular positive electrode)/(rectangular separator)/(rectangularnegative electrode)/(rectangular separator).

The obtained stacked body was wound from an end in lengthwise directionby a winding machine to obtain a wound body. Furthermore, the wound bodywas pressed under the press conditions of a temperature of 70° C. and apressure of 1.0 MPa for 8 seconds to obtain a flat body.

Then, the flat body was wrapped in an aluminum package as a sheathingmaterial for a non-aqueous secondary battery. Subsequently, a spaceformed by the aluminum package was filled with an electrolyte solution(electrolyte: LiPF₆ at a concentration of 1 M, solvent: ethylenecarbonate (EC)/diethyl carbonate (DEC)/vinylene carbonate(VC)=68.5/30/1.5 (volume ratio)) in such a manner that the air does notremain. Furthermore, the opening of the aluminum package was heat sealedat 150° C. to seal and close the opening of the aluminum sheath. As aresult, a wound type lithium ion secondary battery (I) was produced as anon-aqueous secondary battery. The capacity of this non-aqueoussecondary battery was 800 mAh.

The obtained non-aqueous secondary battery was evaluated forlow-temperature output properties and life properties.

Example 2

A non-aqueous secondary battery and its constituent elements wereproduced and evaluated by the same operation as that in Example 1 exceptthat the following matter was changed.

-   -   The monomer composition in (1-2) was changed to a composition        containing 80 parts of styrene (St), 15 parts of n-butyl        acrylate (BA), 4 parts of methacrylic acid (MAA), and 1 part of        ethylene dimethacrylate (EDMA).

Example 3

A non-aqueous secondary battery and its constituent elements wereproduced and evaluated by the same operation as that in Example 1 exceptthat the following matter was changed.

-   -   The monomer composition in (1-2) was changed to a composition        containing 55 parts of styrene (St), 40 parts of n-butyl        acrylate (BA), 4 parts of methacrylic acid (MAA), and 1 part of        ethylene dimethacrylate (EDMA).

Example 4

A non-aqueous secondary battery and its constituent elements wereproduced and evaluated by the same operation as that in Example 1 exceptthat the following matter was changed.

-   -   The monomer composition in (1-2) was changed to a composition        containing 20 parts of styrene (St), 75 parts of n-butyl        acrylate (BA), 4 parts of methacrylic acid (MAA), and 1 part of        ethylene dimethacrylate (EDMA).

Example 5

A non-aqueous secondary battery and its constituent elements wereproduced and evaluated by the same operation as that in Example 1 exceptthat the following matter was changed.

-   -   The monomer composition in (1-2) was changed to a composition        containing 75.99 parts of styrene (St), 20 parts of n-butyl        acrylate (BA), 4 parts of methacrylic acid (MAA), and 0.01 part        of ethylene dimethacrylate (EDMA).

Example 6

A non-aqueous secondary battery and its constituent elements wereproduced and evaluated by the same operation as that in Example 1 exceptthat the following matter was changed.

-   -   The monomer composition in (1-2) was changed to a composition        containing 75 parts of styrene (St), 20 parts of n-butyl        acrylate (BA), 3 parts of methacrylic acid (MAA), and 2 part of        ethylene dimethacrylate (EDMA).

Example 7

A non-aqueous secondary battery and its constituent elements wereproduced and evaluated by the same operation as that in Example 1 exceptthat the following matter was changed.

-   -   The monomer composition in (1-2) was changed to a composition        containing 75 parts of styrene (St), 20 parts of n-butyl        acrylate (BA), 4.6 parts of methacrylic acid (MAA), and 0.4 part        of allyl methacrylate (AMA).

Example 8

A non-aqueous secondary battery and its constituent elements wereproduced and evaluated by the same operation as that in Example 1 exceptthat the following matter was changed.

-   -   The amount of the emulsifier in (1-2) was changed to 1.2 parts,        to thereby adjust the volume-average particle diameter D of the        obtained particulate polymer to 0.5 μm.

Example 9

(9-1. Preparation of Particulate Polymer for Functional Layer)

Into a 5 MPa pressure resistant container equipped with a stirrer, amonomer composition, 1.2 parts of sodium dodecylbenzenesulfonate as anemulsifier, 150 parts of ion exchanged water, and 0.5 part of potassiumpersulfate as a polymerization initiator were charged. The mixture wassufficiently stirred, and then warmed to 60° C. The monomer compositionwas prepared as a composition containing 75 parts of styrene (St), 20parts of n-butyl acrylate (BA), 4 parts of methacrylic acid (MAA), and 1part of ethylene glycol dimethacrylate (EDMA). In this manner, thepolymerization of the polymerizable monomers was initiated. At the timepoint when the polymerization conversion rate reached 96%, the reactionmedium was cooled to stop the polymerization reaction. As a result, anaqueous dispersion liquid containing seed particles was prepared.

An additional monomer composition was further added to the aqueoussolution of the seed particles. The additional monomer composition wasprepared as a composition containing 75,000 parts of styrene (St),20,000 parts of n-butyl acrylate (BA), 4,000 parts of methacrylic acid(MAA), and 1,000 parts of ethylene glycol dimethacrylate (EDMA). Themixture was sufficiently stirred, and then warmed to 60° C. In thismanner, the polymerization of the polymerizable monomers was initiated.At the time point when the polymerization conversion rate reached 96%,the reaction medium was cooled to stop the polymerization reaction. As aresult, an aqueous dispersion liquid containing a particulate polymerhaving a volume-average particle diameter of 5.0 μm was prepared.

The volume-average particle diameter D, swelling degree S, elutionamount X, and glass transition temperature of the obtained particulatepolymer were measured.

(9-2. Production and Evaluation of Non-Aqueous Secondary Battery etc.)

A non-aqueous secondary battery and its constituent elements wereproduced and evaluated by the same operation as that in (1-1) and (1-3)to (1-10) of Example 1 except that the following matter was changed.

-   -   The product obtained in (9-1) was used instead of that obtained        in (1-2) as the aqueous dispersion liquid of the particulate        polymer.

Example 10

A non-aqueous secondary battery and its constituent elements wereproduced and evaluated by the same operation as that in Example 1 exceptthat the following matters were changed.

-   -   No inorganic particles were used in (1-3).    -   The amount of the particulate polymer used in (1-3) was changed        to 100 parts by weight.

Example 11

A non-aqueous secondary battery and its constituent elements wereproduced and evaluated by the same operation as that in Example 1 exceptthat the following matters were changed.

-   -   In (1-3), 76 parts by weight of boehmite (“(trade name) BMM”        manufactured by Kawai Lime Industry Co., Ltd.; number-average        particle diameter 0.9 μm; density 3.5 g/cm³; (hydrate of        aluminum oxide: AlOOH)) was used instead of 80 parts by weight        of alumina as inorganic particles.    -   The amount of the particulate polymer used in (1-3) was changed        to 24 parts by weight.

Example 12

A non-aqueous secondary battery and its constituent elements wereproduced and evaluated by the same operation as that in Example 1 exceptthat the following matters were changed.

-   -   The amount of the inorganic particles used in (1-3) was changed        to 49 parts by weight.    -   The amount of the particulate polymer used in (1-3) was changed        to 51 parts by weight.

Example 13

A non-aqueous secondary battery and its constituent elements wereproduced and evaluated by the same operation as that in Example 1 exceptthat the following matters were changed.

-   -   The amount of the inorganic particles used in (1-3) was changed        to 94 parts by weight.    -   The amount of the particulate polymer used in (1-3) was changed        to 6 parts by weight.

Example 14

(14-1. Preparation of Positive Electrode Having Functional Layer)

The slurry composition for a functional layer obtained in (1-3) wasapplied onto one surface of the positive electrode obtained in (1-9) ofExample 1 such that the thickness thereof became 2 μm. Thereafter, itwas dried at 50° C. for 10 minutes. Accordingly, a functional layer fora non-aqueous secondary battery was formed on one surface of thepositive electrode. Subsequently, the functional layer for a non-aqueoussecondary battery was also formed on the other surface of the positiveelectrode by the same operation as the aforementioned operation.Accordingly, a positive electrode having a functional layer whichincluded a current collector, a positive electrode mixture layerdisposed on both surfaces of the current collector, and a functionallayer for a non-aqueous secondary battery disposed on each of thepositive electrode mixture layers was obtained. In the obtained positiveelectrode having a functional layer, the thickness of each of thefunctional layers was 2.0 μm. The obtained positive electrode having afunctional layer was evaluated for blocking properties.

(14-2. Preparation of Separator)

A separator having a functional layer for a non-aqueous secondarybattery was obtained by the same operation as that of (1-4) in Example 1except that the functional layer for a non-aqueous secondary battery wasformed not on both surfaces but on only one surface of the separatorsubstrate. The obtained separator had a separator substrate and afunctional layer for a non-aqueous secondary battery disposed on onlyone surface of the separator substrate. The obtained separator and thepositive electrode obtained in (14-1) were evaluated for adhesiveness.

(14-3. Production of Non-Aqueous Secondary Battery)

A non-aqueous secondary battery was produced and evaluated by the sameoperation as that of (1-10) in Example 1 except that the followingmatters were changed.

-   -   The positive electrode having a functional layer obtained in        (14-1) was used instead of the positive electrode obtained in        (1-9).    -   The separator obtained in (14-2) was used instead of the        separator obtained in (1-4).    -   In a stacked body having the layer structure of (rectangular        positive electrode)/(rectangular separator)/(rectangular        negative electrode)/(rectangular separator), the direction of        the rectangular separator was such that the functional        layer-side surface thereof faced the rectangular negative        electrode.

Example 15

(15-1. Preparation of Negative Electrode Having Functional Layer)

The slurry composition for a functional layer obtained in (1-3) ofExample 1 was applied onto one surface of the negative electrodeobtained in (1-7) of Example 1 such that the thickness thereof became 2μm. Thereafter, it was dried at 50° C. for 10 minutes. Accordingly, afunctional layer for a non-aqueous secondary battery was formed on onesurface of the negative electrode. Subsequently, the functional layerfor a non-aqueous secondary battery was also formed on the other surfaceof the negative electrode by the same operation as the aforementionedoperation. Accordingly, a negative electrode having a functional layerwhich included a current collector, a negative electrode mixture layerdisposed on both surfaces of the current collector, and a functionallayer for a non-aqueous secondary battery disposed on each of thenegative electrode mixture layers was obtained. In the obtained negativeelectrode having a functional layer, the thickness of each functionallayer was 2.0 μm. The obtained negative electrode having a functionallayer was evaluated for blocking properties.

(15-2. Production of Non-Aqueous Secondary Battery)

A non-aqueous secondary battery and its constituent elements wereproduced and evaluated by the same operation as that of (1-10) inExample 1 except that the following matters were changed.

-   -   The negative electrode having a functional layer obtained in        (15-1) was used instead of the negative electrode obtained in        (1-7).    -   The separator obtained in (14-2) of Example 14 was used instead        of the separator obtained in (1-4). The evaluation for        adhesiveness was performed on the obtained separator and the        positive electrode obtained in (15-1).    -   In a stacked body having the layer structure of (rectangular        positive electrode)/(rectangular separator)/(rectangular        negative electrode)/(rectangular separator), the direction of        the rectangular separator was such that the separator        substrate-side surface thereof faced the rectangular negative        electrode.

Comparative Example 1

A non-aqueous secondary battery and its constituent elements wereproduced and evaluated by the same operation as that in Example 1 exceptthat the following matter was changed.

-   -   The monomer composition in (1-2) was changed to a composition        containing 75 parts of styrene (St), 20 parts of n-butyl        acrylate (BA), and 4 parts of methacrylic acid (MAA) (ethylene        dimethacrylate was not used).

Comparative Example 2

A non-aqueous secondary battery and its constituent elements wereproduced and evaluated by the same operation as that in Example 1 exceptthat the following matter was changed.

-   -   The monomer composition in (1-2) was changed to a composition        containing 85.9 parts of styrene (St), 10 parts of n-butyl        acrylate (BA), 4 parts of methacrylic acid (MAA), and 0.1 part        of allyl methacrylate (AMA).

Comparative Example 3

A non-aqueous secondary battery and its constituent elements wereproduced and evaluated by the same operation as that in Example 1 exceptthat the following matter was changed.

-   -   The monomer composition in (1-2) was changed to a composition        containing 15.9 parts of styrene (St), 80 parts of n-butyl        acrylate (BA), 4 parts of methacrylic acid (MAA), and 0.1 part        of allyl methacrylate (AMA).

The obtained measurement results and evaluation results of Examples 1 to15 and Comparative Examples 1 to 3 are shown in the following Tables 1to 3.

In Tables 1 to 3, meanings of the abbreviations are as follows.

St: use amount (part) of styrene

BA: use amount (part) of n-butyl acrylate

MMA: use amount (part) of methyl methacrylate

EDMA: use amount (part) of ethylene dimethacrylate

AMA: use amount (part) of allyl methacrylate

Particle Tg: glass transition temperature (° C.) of the particulatepolymer

Inorganic particles: use amount (part) of the inorganic particles inpreparation of the slurry composition for a functional layer. As toExample 1, the use amount of boehmite. As to others, the use amount ofalumina.

Particulate polymer: use amount (part) of the particulate polymer inpreparation of the slurry composition for a functional layer

Swelling degree S: measured value of the swelling degree for the solidcontent of the slurry composition for a functional layer

Elution amount X: measured value of the elution amount for the solidcontent of the slurry composition for a functional layer

D50: D50 value obtained from the measurement result of thevolume-average particle diameter D of the inorganic particles

Adhesiveness: evaluation result for the adhesiveness of the functionallayer for a non-aqueous secondary battery

Blocking properties: evaluation result for the blocking properties ofthe separator or electrode. As to Example 14, the evaluation result ofthe positive electrode. As to Example 15, the evaluation result of thenegative electrode. As to others, the evaluation result of theseparator.

Low output properties: evaluation result for the low-temperature outputproperties of the non-aqueous secondary battery

Life properties: evaluation result for the life properties of thenon-aqueous secondary battery

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 St (parts) 75 80 55 20 75.9975 BA (parts) 20 15 40 75 20 20 MAA (parts) 4 4 4 4 4 3 EDMA (parts) 1 11 1 0.01 2 AMA (parts) 0 0 0 0 0 0 Particle 60 70 21 −27 60 60 Tg (° C.)Swelling 2.0 1.9 2.2 2.5 3.0 1.5 degree S (times) Elution 0.5 1.0 1.01.0 2.0 0.1 amount X (%) D50 (μm) 0.6 0.6 0.6 0.6 0.6 0.6 Inorganic 8080 80 80 80 80 particles (parts) Particulate 20 20 20 20 20 20 polymer(parts) Adhesiveness A B A B A B Blocking A A B C B A property Low- A AA A B B temperature output property Life A A A A A B property

TABLE 2 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 St (parts) 75 75 75 75 7575 BA (parts) 20 20 20 20 20 20 MAA (parts) 4.6 4 4 4 4 4 EDMA (parts) 01 1 1 1 1 AMA (parts) 0.4 0 0 0 0 0 Particle Tg (° C.) 60 60 60 60 60 60Swelling 1.5 2.0 2.0 2.0 2.0 2.0 degree S (times) Elution amount 0.1 0.50.5 0.5 0.5 0.5 X (%) D50 (μm) 0.6 0.5 5.0 0.6 0.6 0.6 Inorganic 80 8080 0 76 49 particles (parts) Particulate 20 20 20 100 24 51 polymer(parts) Adhesiveness A A A A A A Blocking A A B B A B property Low- A BB B B C temperature output property Life property A A A B A B

TABLE 3 Ex. Comp. Comp. Comp. Ex. 13 Ex. 14 15 Ex. 1 Ex. 2 Ex. 3 St(parts) 75 75 75 75 85.9 15.9 BA (parts) 20 20 20 20 10 80 MAA (parts) 44 4 4 4 4 EDMA (parts) 1 1 1 0 0 0 AMA (parts) 0 0 0 0 0.1 0.1 ParticleTg (° C.) 60 60 60 60 82 −32 Swelling 2.0 2.0 2.0 12 1.8 2.6 degree S(times) Elution amount 0.5 0.5 0.5 12 1.0 2.5 X (%) D50 (μm) 0.6 0.6 0.60.6 0.6 0.6 Inorganic 94 80 80 80 80 80 particles (parts) Particulate 620 20 20 20 20 polymer (parts) Adhesiveness B A A C C C Blocking A A A CB C property Low- A B B C B B temperature output property Life propertyA A A E E E

(Discussion)

As understood from the results of Table 1 to Table 3, in Examples inwhich the particulate polymer satisfies the requirements of the presentinvention, excellent results of adhesiveness, blocking properties,low-temperature output properties, and life properties which arebalanced well can be obtained. On the contrary, in Comparative Example 1in which the swelling degree is outside the range defined by the presentinvention, and Comparative Examples 2 and 3 in which the composition ofmonomer units is outside the range defined by the present invention,evaluation results inferior to Examples were obtained.

The invention claimed is:
 1. A composition for a non-aqueous secondarybattery functional layer comprising a particulate polymer, wherein theparticulate polymer is a copolymer containing 20% by weight or more and80% by weight or less of an aromatic monovinyl monomer unit; and 0.01%by weight or more and 2% by weight or less of a polyvalent ethylenicallyunsaturated crosslinkable monomer unit, a volume-average particlediameter D of the particulate polymer is 0.5 μm or more and 5 μm orless, a swelling degree of the particulate polymer to an electrolytesolution is more than 1 time and 3 times or less, and the particulatepolymer has only one glass transition temperature and the only one glasstransition temperature of the particulate polymer is 20° C. or higher.2. The composition for the non-aqueous secondary battery functionallayer according to claim 1, wherein an elution amount of the particulatepolymer to the electrolyte solution is 0.01% by weight or more and 10%by weight or less.
 3. The composition for the non-aqueous secondarybattery functional layer according to claim 1, further comprisinginorganic particles.
 4. A functional layer for a non-aqueous secondarybattery formed using the composition for the non-aqueous secondarybattery functional layer according to claim
 1. 5. A non-aqueoussecondary battery comprising a positive electrode, a negative electrode,a separator, and an electrolyte, wherein one or more of the positiveelectrode, the negative electrode, and the separator have the functionallayer for the non-aqueous secondary battery according to claim
 4. 6. Afunctional layer for the non-aqueous secondary battery comprising aparticulate polymer, wherein the particulate polymer is a copolymercontaining 20% by weight or more and 80% by weight or less of anaromatic monovinyl monomer unit; and 0.01% by weight or more and 2% byweight or less of a polyvalent ethylenically unsaturated crosslinkablemonomer unit, a volume-average particle diameter of the particulatepolymer is 0.5 μm or more and 5 μm or less, a swelling degree of theparticulate polymer to a specific electrolyte solution is more than 1time and 3 times or less, and the particulate polymer has only one glasstransition temperature and the only one glass transition temperature ofthe particulate polymer is 20° C. or higher.
 7. The composition for thenon-aqueous secondary battery functional layer according to claim 1,wherein the particulate polymer further contains 5% by weight or moreand 20% by weight or less of a (meth)acrylic acid alkyl ester monomerunit.
 8. The functional layer for the non-aqueous secondary batteryaccording to claim 6, wherein the particulate polymer further contains5% by weight or more and 20% by weight or less of a (meth)acrylic acidalkyl ester monomer unit.